During device packaging, electrical connections must be formed between semiconductor device electrode pads of a substrate die and package lead frames. One technique for forming such electrical connections is to employ a Flip Chip process.
During a typical Flip Chip process, conductive bumps are provided at electrode pads of a substrate die, and the substrate die is attached to a circuit board or other carrier face down. The conductive bumps form electrical and mechanical connections between the substrate die and the carrier. Various reflow and/or underfill processes may be employed to secure the substrate die to the underlying carrier and protect the electrical connections provided by the conductive bumps.
Flip Chip bumps may be formed at electrode pads of a substrate using many techniques such as masked physical vapor deposition, electrochemical or electroless plating, paste printing or the like. Another technique for forming bumps at electrode pads of a substrate is to pre-form micron size solder balls and to transfer the pre-formed solder balls to the electrode pads. E. Hashino et al., “Micro-Ball Wafer Bumping for Flip Chip Interconnection,” IEEE Electronic Components and Technology Conference (2001) describe such a technique in which pre-formed solder balls are transferred to electrode pads via an arrangement plate. As described by E. Hashino et al., the arrangement plate includes a plurality of vacuum holes, each adapted to vacuum-hold one solder ball, arranged in a pattern that matches the pattern of electrode pads to which the solder balls are to be transferred. Ideally, such an approach allows all solder balls required for a substrate to be transferred to the electrode pads of the substrate in one transfer operation.
Vacuum-based arrangement plates suffer from several drawbacks. For example, a unique arrangement plate typically must be employed for each electrode pad pattern. Also, during transfer of solder balls to the arrangement plate, improper solder ball registration may occur at one or more vacuum holes of the arrangement plate due to vacuum leaks, contamination, moisture, etc. To affect transfer of solder balls from the arrangement plate to electrode pads of a substrate, an adhesive agent such as solder flux typically must be employed at each electrode pad so that solder balls remain at the electrode pads when the arrangement plate is removed. Flux-free processing thereby is precluded. Accordingly, improved methods and apparatus for transferring conductive materials, such as solder balls, are desirable.